The folder of a web printing press cuts and arranges signatures which are printed on a continuous web of material, such as paper. However, the cutting device of the folder often may fall into misalignment with the image on the web, cutting the web at the improper time. The image on the resulting signatures will be lengthwise off-center, or even partially cut off, often creating a large amount of unusable or poor quality signatures. It is therefore important to cut the web at a proper place, i.e. to keep the images on the web in register with the cutting device of the folder.
Methods and devices for maintaining the proper print to cut register are known. One such device is the Microtrak 9500 sold by Web Printing Controls, Inc. Its method of operation involves having a cutter cut the web at constant intervals, and altering the web position with a conventional web compensator to maintain register. A web scanner senses the position of the image as it enters the folder. The cutter position is monitored by a reference generator. If the position of the image is out of register with the cutter position, the web is moved forward or backward by the web compensator by the desired amount to restore register. The web compensator motor therefore "clicks" the web compensator up or down a set amount to move the web forward or backward. As stated in the manual of this device, compensation of this device also occasionally may be maintained by the cutter by leaving the scanner input constant and mechanically changing the cutter's phase in relation to the print.
The above-mentioned device and method has the drawback that the scanner is located far from the cutter and all disturbances which occur in machinery between the scanner and the cutter are ignored. Typically, 50 to 100 feet of web may run between the scanner and the cutter.
Moreover, the response time of the above-mentioned device is often insufficient to eliminate print to cut registration defects in faster presses.